The present invention relates to improved systems and methods for the deactivation of contaminants, i.e., organisms (biological contaminants) or chemical contaminants.
Fresh meats, fruits, vegetables, and other food products, for example beef carcasses, accumulate organisms, which as used herein includes bacteria, viruses, and fungi, from the air, ground, water and other sources with which they come into contact. These organisms, through various known mechanisms, cause the perishable food products to spoil, thereby significantly limiting the shelf-life of the food products. (Shelf-life is the period of time during which the perishable food product can be stored refrigerated or unrefrigerated, and remain edible and free from noticeable or harmful degradation or contamination by organisms.) As a result, methods and apparatuses suitable for deactivating, i.e., killing or sterilizing, such organisms and thereby extending the shelf-life of perishable foods, such as meats and other edible food products, are desirable.
The photobiological effects of light, including infrared light (780 nm to 2600 nm; i.e., 3.9.times.10.sup.14 Hz to 1.2.times.10.sup.14 Hz), visible light (380 to 780 nm; i.e., 7.9.times.10.sup.14 Hz to 3.9.times.10.sup.14 Hz), near ultraviolet light (300 to 380 nm; i.e., 1.0.times.10.sup.15 Hz to 7.9.times.10.sup.14 Hz) and far ultraviolet light (170 to 300 nm; i.e., 1.8.times.10.sup.15 Hz to 1.0.times.10.sup.15 Hz), have been studied, and efforts have been made to employ light to deactivate organisms on food products and packaging materials for food products. See, e.g., U.S. Pat. No. 4,871,559, issued to Dunn et al. (the '559 patent), incorporated herein by reference. Systems and methods employing the photobiological effects of light to deactivate, i.e., kill or sterilize, substantially all (i.e., more than 50%, e.g., 90%, deactivation rate) of the organisms on the surface of the food product and/or packaging material have proven to be effective in extending the shelf-life of perishable food products.
One improvement to systems that utilize the photobiological effects of light to effect deactivation of organisms on food products or food packaging materials is to treat the food product or food packaging material with an absorption enhancing agent prior to the illumination of the food product or packaging material. See e.g., the '559 patent. Absorption enhancing agents have a high optical absorption coefficient at least a portion of the spectral wavelengths with which the food product or packaging material is to be illuminated.
Another improvement to systems that utilize the photobiological effects of light to effect deactivation of organisms on food products is to subject the food product to a high pressure water wash prior to the illumination of the food product. See e.g., the '559 patent. The high pressure water wash physically removes some organisms from the surface of the food product prior to the illumination.
While these improvements to systems and methods that employ the photobiological effects of light to effect a prescribed level of deactivation of organisms on food products or food packaging materials are advantageous, further improvements in the deactivation rate, reduction of the time required to achieve a desired deactivation rate, and/or reduction of the energy needed to effect deactivation or kill are needed and highly desirable.
Photocatalytic effects have also been studied for bactericidal action. See Sabate, et al., "A Kinetic Study of the Photocatalytic Degradation of 3-Chlorosalicylic Acid over TiO.sub.2 Membranes Supported on Glass", Journal of Catalysis, 127:167-177 (1991); Saito, et al., "Mode of Photocatalytic Bactericidal Action of Powdered Semiconductor TiO.sub.2 on Mutans Streptococci", J. Photochem. Photobiol. B: Biol. 14:369-379 (1992); Ireland, et al., "Inactivation of Escherichia Coli by Titanium Dioxide Photocatalytic Oxidation", Applied and Environmental Microbiology, 59:5, pp. 1668-1670 (May 1993); Glaskin, "Kill the Bugs to Cure the Building", New Scientist, pp. 22 (Mar. 11, 1995); and "Using Photocatalysts, Japanese Firm Develops Antibacterial Tiles and Sanitary Ware", Tile Industry News, pp. 1, (May/June 1995), all of which are incorporated herein by reference.
Specifically, photocatalytic effects that result in the production of highly reactive agents (defined herein to mean superoxide ions and/or hydroxyl radicals (HO.sup.-) (produced as a result of the cleavage of air or water)) have been the subject of research relating to the deactivation of contaminants, i.e., organisms (or biological contaminants) or chemical contaminants. This research has centered around the use of anatase titanium dioxide illuminated with light of wavelengths less than about 400 nm for extended periods of time (e.g., from several minutes to several days). Problematically, these highly reactive agents, i.e., the superoxide ions or hydroxyl radicals, are very short lived, due to their highly reactive nature. As a result, photocatalytic effects are effective in deactivating only contaminants located very near to, i.e., within an effective range of, the catalyst, i.e., titanium dioxide. Thus, while these studies have shown that photocatalytic effects offer some promise in the deactivation of contaminants, further improvements are needed to assure that contaminants located beyond the effective range of these effects are deactivated.
The present invention advantageously improves upon heretofore known systems and methods employing the photobiological effects of light, or, alternatively, photocatalytic effects, to deactivate contaminants.